CA1108971A - Method for minimizing carbon formation on methanation catalysts - Google Patents
Method for minimizing carbon formation on methanation catalystsInfo
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- CA1108971A CA1108971A CA306,146A CA306146A CA1108971A CA 1108971 A CA1108971 A CA 1108971A CA 306146 A CA306146 A CA 306146A CA 1108971 A CA1108971 A CA 1108971A
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Abstract
ABSTRACT OF THE DISCLOSURE
A method for controlling carbon formation on meth-anation catalysts by determining the carbon formation potential for the reaction system and adjusting the composition, tempera-ture and pressure of the inlet reactant streams to maintain the carbon deposition potential for the reaction system below 40F°.
A method for controlling carbon formation on meth-anation catalysts by determining the carbon formation potential for the reaction system and adjusting the composition, tempera-ture and pressure of the inlet reactant streams to maintain the carbon deposition potential for the reaction system below 40F°.
Description
Case: ICR 2753 This invention relates to methods for predictiny car~on formation on methanation catalysts.
This invention also relates to methods for control~ing carbon formation on methanation catal~sts.
This invention also relates to methods for minimizing carbon formation in methanation catalyst heds used for methanation reactions.
This invention also relates to methods for removing carbon from methanation catalysts.
In recent years, there has been increased interest in the production of synthetic fuels such as methane from sources other than petroleum. As is well known, there have recently been shortages in the supply of petroleum and natural gas and it is apparent that other sources of fuels will be required in the future. As a result of the continuing need for natural gas, considerable effort has been directed to the development of methods for producing synthetic natural gas from carbonaceous solids such as coal and the like. Typically, such processes comprise passing at least a portion of a gaseous stream com-prising hydrogen and carbon monoxide produced by the partial oxidation of a hydrocarbonaceous fuel to a water-gas shift reactor to produce a gaseous stream rich in hydrogen and carbon dioxide. Acid gases such as carbon dioxide and hydrogerl sulfide $~
.
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Case: ICR 2753 are then removed leaving a hydrogen-rich gas stream at least a portion of which is then combined with a hydrogen- and carbon monoxide-containing stream to produce a gaseous feed for a methanation reactor. The acid gases are also normally rernoved from the hydrogen and carbon monoxide-containing stream mixed with the hydrogen-rich stream. The resulting carbon monoxide-and hydrogen-containing stream is then passed to a methanation reactor where it reacts under appropriate reaction conditions to form methane. Considerable effort has been directed to the development of such processes and one such process is described in U.S. Patent 3,922,148 issued November 25, 1975 to Child.
In such processes, it has been found that a continuing problem is the tendency of mixtures of carbon oxides and hydrogen to form carbon in the catalyst bed under reaction conditions not greatly dissimilar to those required for the production of methane. ~s a result, there has been a continuing effort directed to the development of methods which will define carbon forming conditions in the catalyst bed in order that longer catalyst life may be accomplished.
- It has now been found that carbon formation in methana-tion catalyst beds can be controlled by a method comprising, determining the carbon-forminy potential of the reaction system and adjusting the reactant :tream oomposition, temperature and , ~ .
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pressure to a value such that the carbon-forming potential i5 less than 40F. Desirably, the carbon-forming potential will be less than lOF. For carbon removal, the poten-tial will be less than OF~.
FIGURE l shows a reactor containing a methanation catalyst bed;
FIGURE 2 iS a chart showing equilibrium con,stant values determined for a methanation catalyst as a function of temperature for the reac-tion
This invention also relates to methods for control~ing carbon formation on methanation catal~sts.
This invention also relates to methods for minimizing carbon formation in methanation catalyst heds used for methanation reactions.
This invention also relates to methods for removing carbon from methanation catalysts.
In recent years, there has been increased interest in the production of synthetic fuels such as methane from sources other than petroleum. As is well known, there have recently been shortages in the supply of petroleum and natural gas and it is apparent that other sources of fuels will be required in the future. As a result of the continuing need for natural gas, considerable effort has been directed to the development of methods for producing synthetic natural gas from carbonaceous solids such as coal and the like. Typically, such processes comprise passing at least a portion of a gaseous stream com-prising hydrogen and carbon monoxide produced by the partial oxidation of a hydrocarbonaceous fuel to a water-gas shift reactor to produce a gaseous stream rich in hydrogen and carbon dioxide. Acid gases such as carbon dioxide and hydrogerl sulfide $~
.
7~
Case: ICR 2753 are then removed leaving a hydrogen-rich gas stream at least a portion of which is then combined with a hydrogen- and carbon monoxide-containing stream to produce a gaseous feed for a methanation reactor. The acid gases are also normally rernoved from the hydrogen and carbon monoxide-containing stream mixed with the hydrogen-rich stream. The resulting carbon monoxide-and hydrogen-containing stream is then passed to a methanation reactor where it reacts under appropriate reaction conditions to form methane. Considerable effort has been directed to the development of such processes and one such process is described in U.S. Patent 3,922,148 issued November 25, 1975 to Child.
In such processes, it has been found that a continuing problem is the tendency of mixtures of carbon oxides and hydrogen to form carbon in the catalyst bed under reaction conditions not greatly dissimilar to those required for the production of methane. ~s a result, there has been a continuing effort directed to the development of methods which will define carbon forming conditions in the catalyst bed in order that longer catalyst life may be accomplished.
- It has now been found that carbon formation in methana-tion catalyst beds can be controlled by a method comprising, determining the carbon-forminy potential of the reaction system and adjusting the reactant :tream oomposition, temperature and , ~ .
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pressure to a value such that the carbon-forming potential i5 less than 40F. Desirably, the carbon-forming potential will be less than lOF. For carbon removal, the poten-tial will be less than OF~.
FIGURE l shows a reactor containing a methanation catalyst bed;
FIGURE 2 iS a chart showing equilibrium con,stant values determined for a methanation catalyst as a function of temperature for the reac-tion
2 CO j~ C ~ C02;
FIGURE 3 is a chart showing equilibrium constant values determined for a methanation catalyst as a function of temperature for the reaction CH4 ~ C + 2H2; and, FIGURE 4 shows the inlet pressure increase with time during the plugging of a reactor during a test.
The invention is directed to a method for detecting and reducing carbon formation in a catalyst bed wherein carbon oxides are reacted with hydrogen to produce methane, the method consisting essentially of:
(a) monitoring the differential pressure across said catalyst bed; and (b) adjusting the carbon deposition potential to carbon removal conditions when the differential pressure increases above a desired value.
The present invention is also directed to a method for controlling carbon formation in a catalyst bed ~Jherein carbon oxides are reacted with hydrogen to produce methane, the method consistiny essentially of:
(a) determining the composition, temperature and pressure of the inlet reactant stream;
(b) determining the equilibrium reaction product stream j;. ~
- , . .
.. . .
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composition, temperature and pressure based on the simultan-eous equilibrium of the following reactions:
~1) CO + 3 H2 ~ CH~ ~ H20 (2) C0 + H20 ~ C2 + H2 ) 2 + 4 H2 ~- CH4 + 2 H20;
(c) determining the reaction equilibrium constant Kl = ~ 2 for the react.ion;
(4) 2 C0 ~ C + C02 wherein W = equals the mol fraction C02 in the equilibrium reaction product stream of (b), Pl - the pressure of the equilibrium product reaction stream of (b), and X = the mol fraction C0 in the equilibrium reaction product stream of (b);
(d) determining the reaction equilibrium constant K2 = T 1 for the reaction (5) CH4 ~- C + 2 H2 wherein Y = the mol fraction hydrogen in the equilibrium ; reaction product stream of (b), Pl = the pressure of the equilibrium reaction product stream of (b), and Z = the mol raction methane in the equilibrium reaction product stream of (b);
(e) determining the equilibrium temperature (Tl) in the reaction product stream;
: () comparing the equilibrium temperature (Tl) in the :~ reaction product stream to the equilibrium temperature (Tkl) corresponding to Kl o (c) and determining the carbon formation potential Cl which is defined as:
(6) Cl = Tkl Tl;
4a -(g) comparing -the equilibrium -temperature in the reaction product stream to the equilibrium temperature ('rk2) corresponding to K2 of (d) and determining the carbon formation potential C2 wh~ch is defined as:
(7) C2 = Tl Tk2;
(h) adding Cl and C2 to obtain a carbon deposition potential for the reaction; and (i) a~usting the composition, temperature and pressure of the inlet reactant stream so that the carbon deposition potential for the reaction is less -than 40F.
Many methods have been propGsed for determining the reaction conditions which result in coke formation in a methanation catalyst bed; however, such prior methods have, in the main, been ineffective and as a result, the determina-tion of when the methanation reaction system is operating in a carbon-forming zone is left to a large extent to trial . and error. As a result of the need to vary reaction conditions to optimize the reaction efficiency and the like, a considerable amount of time has been directed to the develop-ment of methods for predicting the carbon deposition tendency of a given set of reactor conditions.
; With respect to FIGURE l, a methanation reactor lO
including a catalyst bed 12 is shown with an inlet 18 and an outlet 20 for passing a reactant stream into catalyst bed 12 via inlet 18 and recovering a reaction product stream via outlet 20. In normal operation, a reactant stream is charged into a first end 14 of reactor lO and passes into catalyst bed 12. A reaction zone 22 is normally sharply d~fined by a rapid temperature increase to a substantially constant temperature which continues throughout reactor 10 (adiabatic) as the gaseous product stream flows on to a second end 16 of reactor lO and to outlet 20. It has been observed that carbon ~ormation occurs downstream of the reaction zone 22.
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Thus it could readily be concluded that the carbon formation occurs primarily as a result of the composition, temperature and pressure conditions in the product stream rather than the reactant stream. The problem is o~ a complex nature since many competing reactions are involved and reaction kinetics, thermodynamic equilibria and the like must be considered to determine which of the competing reactions ~;rill occur.
- 5a -...~i Case: IC~ 2753 For instance, the primary reactions in the reaction æone, i.e.
(1) C0 -~ 3H2 ~ CH,I + H20 (2) C0 + H20 ~ C02 -~ H2
FIGURE 3 is a chart showing equilibrium constant values determined for a methanation catalyst as a function of temperature for the reaction CH4 ~ C + 2H2; and, FIGURE 4 shows the inlet pressure increase with time during the plugging of a reactor during a test.
The invention is directed to a method for detecting and reducing carbon formation in a catalyst bed wherein carbon oxides are reacted with hydrogen to produce methane, the method consisting essentially of:
(a) monitoring the differential pressure across said catalyst bed; and (b) adjusting the carbon deposition potential to carbon removal conditions when the differential pressure increases above a desired value.
The present invention is also directed to a method for controlling carbon formation in a catalyst bed ~Jherein carbon oxides are reacted with hydrogen to produce methane, the method consistiny essentially of:
(a) determining the composition, temperature and pressure of the inlet reactant stream;
(b) determining the equilibrium reaction product stream j;. ~
- , . .
.. . .
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composition, temperature and pressure based on the simultan-eous equilibrium of the following reactions:
~1) CO + 3 H2 ~ CH~ ~ H20 (2) C0 + H20 ~ C2 + H2 ) 2 + 4 H2 ~- CH4 + 2 H20;
(c) determining the reaction equilibrium constant Kl = ~ 2 for the react.ion;
(4) 2 C0 ~ C + C02 wherein W = equals the mol fraction C02 in the equilibrium reaction product stream of (b), Pl - the pressure of the equilibrium product reaction stream of (b), and X = the mol fraction C0 in the equilibrium reaction product stream of (b);
(d) determining the reaction equilibrium constant K2 = T 1 for the reaction (5) CH4 ~- C + 2 H2 wherein Y = the mol fraction hydrogen in the equilibrium ; reaction product stream of (b), Pl = the pressure of the equilibrium reaction product stream of (b), and Z = the mol raction methane in the equilibrium reaction product stream of (b);
(e) determining the equilibrium temperature (Tl) in the reaction product stream;
: () comparing the equilibrium temperature (Tl) in the :~ reaction product stream to the equilibrium temperature (Tkl) corresponding to Kl o (c) and determining the carbon formation potential Cl which is defined as:
(6) Cl = Tkl Tl;
4a -(g) comparing -the equilibrium -temperature in the reaction product stream to the equilibrium temperature ('rk2) corresponding to K2 of (d) and determining the carbon formation potential C2 wh~ch is defined as:
(7) C2 = Tl Tk2;
(h) adding Cl and C2 to obtain a carbon deposition potential for the reaction; and (i) a~usting the composition, temperature and pressure of the inlet reactant stream so that the carbon deposition potential for the reaction is less -than 40F.
Many methods have been propGsed for determining the reaction conditions which result in coke formation in a methanation catalyst bed; however, such prior methods have, in the main, been ineffective and as a result, the determina-tion of when the methanation reaction system is operating in a carbon-forming zone is left to a large extent to trial . and error. As a result of the need to vary reaction conditions to optimize the reaction efficiency and the like, a considerable amount of time has been directed to the develop-ment of methods for predicting the carbon deposition tendency of a given set of reactor conditions.
; With respect to FIGURE l, a methanation reactor lO
including a catalyst bed 12 is shown with an inlet 18 and an outlet 20 for passing a reactant stream into catalyst bed 12 via inlet 18 and recovering a reaction product stream via outlet 20. In normal operation, a reactant stream is charged into a first end 14 of reactor lO and passes into catalyst bed 12. A reaction zone 22 is normally sharply d~fined by a rapid temperature increase to a substantially constant temperature which continues throughout reactor 10 (adiabatic) as the gaseous product stream flows on to a second end 16 of reactor lO and to outlet 20. It has been observed that carbon ~ormation occurs downstream of the reaction zone 22.
,,~ , 7~
Thus it could readily be concluded that the carbon formation occurs primarily as a result of the composition, temperature and pressure conditions in the product stream rather than the reactant stream. The problem is o~ a complex nature since many competing reactions are involved and reaction kinetics, thermodynamic equilibria and the like must be considered to determine which of the competing reactions ~;rill occur.
- 5a -...~i Case: IC~ 2753 For instance, the primary reactions in the reaction æone, i.e.
(1) C0 -~ 3H2 ~ CH,I + H20 (2) C0 + H20 ~ C02 -~ H2
(3) C02 + 4 H2 ~ CH4 + 2 H20 occur very rapidly and are aecountable for the rapid temperature rise in reaction zone 22. The gaseous stream passing from reaction zone 22 can probably be considered as in substantially complete equilibrium based on reactions (1), (2) and (3) above (the calculation of the theoretical equilibrium requires only two of the reactions). As a result, this stream appears to be the stream which results in the formation of earbon downstream of reaction zone 22.
The carbon formation is a complex reaction system which is not completely understood even to the present, but it is believed that the two main earbon-forming reaetions are
The carbon formation is a complex reaction system which is not completely understood even to the present, but it is believed that the two main earbon-forming reaetions are
(4) 2 C0 ~ C ~ C02
(5) C~4 ~ C + 2 H2 As noted, a variety of carbon-forming reactions are possible but it is believed that, while Applicants do not wish to be bound by any particular theory, reactions ~4) and (5) probably aecoun-t for at least a major porti.on of the carhon deposition in many instances. These reac-tions usually oecur at a somewhat `:
~ 6 _ ....
- - ~ . : , , .
:: .. .. .. . . . . ~ ,.
.. . . . . . . . .
Case: ICR 2753 slower pace than reactions (1) and (2) and it has been observed that, while some carbon does form simultaneously with the meth-anation reactions, the maximum carbon formation occurs in the zones of the catalyst bed at the maximum tempera-ture, i.e downstream of the methanation reactions.
It has now been found that the carbon-forming poten-tial of a given methanation reaction system can readily be determined by the calculation of -the carbon-forming potential of the system as set forth below.
Based upon the reactor characteristics, inlet reactant stream composition, temperature and pressure, and assuming that reactions (1), (2) and (3) go to substantial completion, an equilibrium reaction product stream composition, -temperature and pressure can be readily calculated (since the equations shown are not independent, any two can be used for the calculation of equilibrium). Based upon the equilibrium reaction product stream, the equilibrium constants for reactions (4) and (5) are determined according to equations (6) and (7) below:
~ 6 _ ....
- - ~ . : , , .
:: .. .. .. . . . . ~ ,.
.. . . . . . . . .
Case: ICR 2753 slower pace than reactions (1) and (2) and it has been observed that, while some carbon does form simultaneously with the meth-anation reactions, the maximum carbon formation occurs in the zones of the catalyst bed at the maximum tempera-ture, i.e downstream of the methanation reactions.
It has now been found that the carbon-forming poten-tial of a given methanation reaction system can readily be determined by the calculation of -the carbon-forming potential of the system as set forth below.
Based upon the reactor characteristics, inlet reactant stream composition, temperature and pressure, and assuming that reactions (1), (2) and (3) go to substantial completion, an equilibrium reaction product stream composition, -temperature and pressure can be readily calculated (since the equations shown are not independent, any two can be used for the calculation of equilibrium). Based upon the equilibrium reaction product stream, the equilibrium constants for reactions (4) and (5) are determined according to equations (6) and (7) below:
(6) K~ 78~2 ' wherein W - mol fraction carbon dio~ide in the equilibrium reaction product stream, Pl ~ pressure of the equilibrium reaction product stream, X = mol fraction carbon monoxide in the equilibrium reaction produc~ stream.
- ' .. . ' , ' .
, ;. . .
Case: ICR 2753 The second equilibrium constant is calculated as follows:
- ' .. . ' , ' .
, ;. . .
Case: ICR 2753 The second equilibrium constant is calculated as follows:
(7) K2 = (Y3 (Z) 5 wherein Y = mol fraction hydrogen in the equi-llbrlum reactlon product stream, Pl = pressure of the equilibrium reaction product stream, Z - mol fraction methane in the equi-librium reaction product stream.
The equilibrium constant values from equations (6) and (7) above are then used for refe*ence -to charts showing the equilibrium constants for reactions (4) and (5) as a function of temperature for the catalys-t used or the same type catalyst.
Such a chart is shown for reaction (4) in FIG. 2, with a similar chart for reaction (5) being shown in FIG. 3. The temperatures for the reaction systems are thus determined. A comparison of the temperatures so determined to the equilibrium product stream temperature permits the determination of the carbon formation potential for each of the two reactions. The equilibrium product stream temperature and composition may be actually measured when the methanation system is operated or may be calculated as set forth above using reactions (1), (2) and (3) and the reactor characteristics. The calculated product stream temperature will be used when the method of the present invention is used to predict the carbon forming tendency of a given system. The carbon formation potential Cl for reaction (4) is de~ined as:
.
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Case: ICR 2753
The equilibrium constant values from equations (6) and (7) above are then used for refe*ence -to charts showing the equilibrium constants for reactions (4) and (5) as a function of temperature for the catalys-t used or the same type catalyst.
Such a chart is shown for reaction (4) in FIG. 2, with a similar chart for reaction (5) being shown in FIG. 3. The temperatures for the reaction systems are thus determined. A comparison of the temperatures so determined to the equilibrium product stream temperature permits the determination of the carbon formation potential for each of the two reactions. The equilibrium product stream temperature and composition may be actually measured when the methanation system is operated or may be calculated as set forth above using reactions (1), (2) and (3) and the reactor characteristics. The calculated product stream temperature will be used when the method of the present invention is used to predict the carbon forming tendency of a given system. The carbon formation potential Cl for reaction (4) is de~ined as:
.
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Case: ICR 2753
(8) 1 k~
wherein Tk ~ the temperature from FIG. 2 ' utilizing Kl, ~1 = the product stream temperature Clearly, the carbon formation potential Cl will be stated as a temperature ~igure, for instance 25F and Fahrenheit temperature has been used throughout although it is to be clearly understood that, were another temperature system used, such as Centigrade (Celsius), a corresponding conversion to C would be necessary, although it is pointed out that the value given is not a tempera-ture as such and accordingly, the conversion of Fahrenheit, for instance, to Centigrade would involve merely the division of the numerical value given by 1.8. The carbon formation potential C2 for reaction ~5~ is defined as follows:
wherein Tk ~ the temperature from FIG. 2 ' utilizing Kl, ~1 = the product stream temperature Clearly, the carbon formation potential Cl will be stated as a temperature ~igure, for instance 25F and Fahrenheit temperature has been used throughout although it is to be clearly understood that, were another temperature system used, such as Centigrade (Celsius), a corresponding conversion to C would be necessary, although it is pointed out that the value given is not a tempera-ture as such and accordingly, the conversion of Fahrenheit, for instance, to Centigrade would involve merely the division of the numerical value given by 1.8. The carbon formation potential C2 for reaction ~5~ is defined as follows:
(9) C2 = Tl - T~
wherein Tl = the product stream temperature T = the temperature determined from FIG. 3 k2 utilizing K2.
The carbon deposition potential for the methanation reaction system is then determined by adding the two values. As stated previously, it has been found that when the carbon deposition potential for the rnethanation reaction system is below 40F, ~ minimal carbon ~ormation occurs. Deslrably, the value is below lOF. In the normal operation of such systems, values below OF
o~ 71 Case: ICR 2753 may be suitable in some instances but in most instances, values below about -lOF will not be used, with values from O to lOF being more common.
Complications arise when the system is out of balance with respect to either reaction (4) or (5) so that a large positive value is obtained for either reaction.
In such an instance, it is possible that, while the combined total may be below 40F, one or the other of reactions (4) and (5) may continue to result in the deposition of carbon in the catalyst bed. Therefore, it is desirable that neither Cl nor C2 be allowed to rise above a value of 20F, and desirably, the values are 5F or less with the preferred operating values being below OF. Desirably, the overall carbon formation potential for the methanation reaction system is below OF.
When carbon formation occurs or has been indicated by operation for periods of time at carbon formation potential values greater than 40F, attempts to remove carbon can be made by increasing the amount of water or steam in the inlet gas, increasing hydrogen/CO ratio, decreasing the amount of c~rbon ..........................................
.
.: :
wherein Tl = the product stream temperature T = the temperature determined from FIG. 3 k2 utilizing K2.
The carbon deposition potential for the methanation reaction system is then determined by adding the two values. As stated previously, it has been found that when the carbon deposition potential for the rnethanation reaction system is below 40F, ~ minimal carbon ~ormation occurs. Deslrably, the value is below lOF. In the normal operation of such systems, values below OF
o~ 71 Case: ICR 2753 may be suitable in some instances but in most instances, values below about -lOF will not be used, with values from O to lOF being more common.
Complications arise when the system is out of balance with respect to either reaction (4) or (5) so that a large positive value is obtained for either reaction.
In such an instance, it is possible that, while the combined total may be below 40F, one or the other of reactions (4) and (5) may continue to result in the deposition of carbon in the catalyst bed. Therefore, it is desirable that neither Cl nor C2 be allowed to rise above a value of 20F, and desirably, the values are 5F or less with the preferred operating values being below OF. Desirably, the overall carbon formation potential for the methanation reaction system is below OF.
When carbon formation occurs or has been indicated by operation for periods of time at carbon formation potential values greater than 40F, attempts to remove carbon can be made by increasing the amount of water or steam in the inlet gas, increasing hydrogen/CO ratio, decreasing the amount of c~rbon ..........................................
.
.: :
- 10 -,~ , , , 7~
Case: ICR 2753 oxides, decreasing the temperature in the catalyst bed, adjusting the pressure or the like. Clearly, these changes can be made individually or in combination as desired and the bed operated under carbon removal conditions for a period of time to attempt to remove the carbon formed. Carbon rerno~al conditions obviously include carbon deposition potentlal values which are well below OF. The carbon removal conditions can be varied to substantially pure hydrogen etc., but it is preferred that values from about O to about -40F~ be used in order that carbon removal may be achieved while maintaining substantially normal operation. The carbon removal will be more gradual but the gradual removal is achieved during continued operation without radical process modifications. A desirable range is from about -10 to about -40F. As indicated above, the carbon deposition potential can be varied by increasing the hydrogen/CO ratio in the inlet reactant stream, decreasing the mol fraction CO or CO2 in the inlet reactant stream, varying the pressure conditions, increasing the amount of water or steam in the inlet reactant stream, and the like.
It has been observed in numerous test runs at moderate carbon producing conditions, that the carbon ~ormation tends to be rather gradual and the composition of the reaction product gas doe~ not change significantly during the carbon formation.
The catalyst bed pressure drop tends to increase gradually '~, ' . .
7~
Case: ICR 2753 during the carbon deposition up to the point where the reactor is substantially plugged, at which point the flow decreases markedly. Upon shutting down the reactor after carbon plugging, it is extremely difficult to remove the catalyst and in some instances requires jack hammers or similar equipment. As a result, it would be extremely desirable to have some method for detecting the formation of carbon in the catalyst bed prior to the plugging of ~he reactor. It has been observed that the pressure drop increase as a result of carbon formation is v~ry gradual until the reactor is substantially pluyged. FIG. 4 shows the pressure increase with time during a test made under moderate carbon-forming conditions. The reactor ran for several days with an inlet pressure of 352 psig and without any chanye in the pressure drop across the catalyst bed prior to the time shown in - lS FIG. 4. The experimental system used a back pressure controller to maintain a constant product gas pressure, so an increase in the inlet pressure resulted as the catalyst bed pressure drop increased. The maximum pressure attained is approximately 440 psig (31 atm.) since the reactor was fitted wi~h safety equipment which prevented any pressure increase beyond this pressure. Upon reaching a pressure of approximately 440 psig, the flow was decreased by the regulatiny equip~ent rather than permit a higher pressure diEferential. As will be ohvious, the , Case: :~CR 2753 ~ 7~
pressure increase was relatively gradual until ths reactor was nearly closed to flow with the vast majority of the pressure increase occurring during the last one hour.
It has now been found that such difficulties are obviated by the use of a differential pressure sensing means connected to the reactor inlet and the reactor outlet or the like to monitor the pressure drop across the reactor. Upon reaching a pre-determined maximum pressure differential, the reactor should be shut down prior to plugging with carbon.
Obviously, automated controls could be used to shut the reactor down during periods when operators are unavailable. As indicated earlier, it is undesirable that carbon formation in the catalyst bed occur but in some instances, due to equipment upsets, improper inlet gas mixtures, improper operating conditions, or the like~ carbon formation will occur in reactors and while such is undesirable, it is even more undesirable that the reactor be allowed to plug with carbon.
When pressure increases indicating carbon formation are observed, the system should be adjusted to carbon removal conditions to attempt to remove the carbon deposits prior to plugging the reactor, etc. Such adjustments clearly must be made before the carbon deposition has reached crisis proportions.
39~
Case: ICR 2753 Having thus described the method of the present invention by reference to certain preferred embodiments, it is pointed out that these embodiments, while preferred, are illus-trative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. It is anticipated that many such variations and modifications may be considered obvious or desirable by those skilled in the art upon a review of the foregoing description of p~eFerred enbodiments and the following examples.
, ;
Case: ICR 2753 ~8971 EXAMPLE
In a series of test runs the following results were obtained.
TABLE
Time elapsed Sum of carbon before plugging forming potentials (hrs) (F) _ 86 ~5 Table I shows the hours before plugging for the various reactor runs and the sum of carbon-forming potentials for each of the test runs. It will be observed that for those runs wherein the sum of carbon-forming potentials is 40F, longer operation was achieved than in those test runs where the sum of carbon-forming potentials was higher~
In a further series of test runs the following results Z- were obtained.
' ~
~:
, - .
. .
Case: ICR 2753 ~ 8971 TABLE I I
Sum of carbon Test forming potentials Length (F) (hrs.) Comments -20 382 No significant carbon accumulation 7 90 Very little, if any, carbon accumulation.
No carbon accumulation on catalyst A small, but significant amount of carbon accumulation on catalyst It will be observed that when the sum of carbon-forming potentials is lOF or less very minor amounts of carbon accumulation occur. At a value of 30F, small amounts of carbon had accumulated.
The test results above clearly show that when the sum of carbon-forming potentials is 40F~ or below, the carbon formation in the catalyst bed is minimized and it is further shown that when the sum of carbon-forming potentials is below about lOF, very desirable results are achieved.
~aving thus described the present invention, we claim:
: '
Case: ICR 2753 oxides, decreasing the temperature in the catalyst bed, adjusting the pressure or the like. Clearly, these changes can be made individually or in combination as desired and the bed operated under carbon removal conditions for a period of time to attempt to remove the carbon formed. Carbon rerno~al conditions obviously include carbon deposition potentlal values which are well below OF. The carbon removal conditions can be varied to substantially pure hydrogen etc., but it is preferred that values from about O to about -40F~ be used in order that carbon removal may be achieved while maintaining substantially normal operation. The carbon removal will be more gradual but the gradual removal is achieved during continued operation without radical process modifications. A desirable range is from about -10 to about -40F. As indicated above, the carbon deposition potential can be varied by increasing the hydrogen/CO ratio in the inlet reactant stream, decreasing the mol fraction CO or CO2 in the inlet reactant stream, varying the pressure conditions, increasing the amount of water or steam in the inlet reactant stream, and the like.
It has been observed in numerous test runs at moderate carbon producing conditions, that the carbon ~ormation tends to be rather gradual and the composition of the reaction product gas doe~ not change significantly during the carbon formation.
The catalyst bed pressure drop tends to increase gradually '~, ' . .
7~
Case: ICR 2753 during the carbon deposition up to the point where the reactor is substantially plugged, at which point the flow decreases markedly. Upon shutting down the reactor after carbon plugging, it is extremely difficult to remove the catalyst and in some instances requires jack hammers or similar equipment. As a result, it would be extremely desirable to have some method for detecting the formation of carbon in the catalyst bed prior to the plugging of ~he reactor. It has been observed that the pressure drop increase as a result of carbon formation is v~ry gradual until the reactor is substantially pluyged. FIG. 4 shows the pressure increase with time during a test made under moderate carbon-forming conditions. The reactor ran for several days with an inlet pressure of 352 psig and without any chanye in the pressure drop across the catalyst bed prior to the time shown in - lS FIG. 4. The experimental system used a back pressure controller to maintain a constant product gas pressure, so an increase in the inlet pressure resulted as the catalyst bed pressure drop increased. The maximum pressure attained is approximately 440 psig (31 atm.) since the reactor was fitted wi~h safety equipment which prevented any pressure increase beyond this pressure. Upon reaching a pressure of approximately 440 psig, the flow was decreased by the regulatiny equip~ent rather than permit a higher pressure diEferential. As will be ohvious, the , Case: :~CR 2753 ~ 7~
pressure increase was relatively gradual until ths reactor was nearly closed to flow with the vast majority of the pressure increase occurring during the last one hour.
It has now been found that such difficulties are obviated by the use of a differential pressure sensing means connected to the reactor inlet and the reactor outlet or the like to monitor the pressure drop across the reactor. Upon reaching a pre-determined maximum pressure differential, the reactor should be shut down prior to plugging with carbon.
Obviously, automated controls could be used to shut the reactor down during periods when operators are unavailable. As indicated earlier, it is undesirable that carbon formation in the catalyst bed occur but in some instances, due to equipment upsets, improper inlet gas mixtures, improper operating conditions, or the like~ carbon formation will occur in reactors and while such is undesirable, it is even more undesirable that the reactor be allowed to plug with carbon.
When pressure increases indicating carbon formation are observed, the system should be adjusted to carbon removal conditions to attempt to remove the carbon deposits prior to plugging the reactor, etc. Such adjustments clearly must be made before the carbon deposition has reached crisis proportions.
39~
Case: ICR 2753 Having thus described the method of the present invention by reference to certain preferred embodiments, it is pointed out that these embodiments, while preferred, are illus-trative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. It is anticipated that many such variations and modifications may be considered obvious or desirable by those skilled in the art upon a review of the foregoing description of p~eFerred enbodiments and the following examples.
, ;
Case: ICR 2753 ~8971 EXAMPLE
In a series of test runs the following results were obtained.
TABLE
Time elapsed Sum of carbon before plugging forming potentials (hrs) (F) _ 86 ~5 Table I shows the hours before plugging for the various reactor runs and the sum of carbon-forming potentials for each of the test runs. It will be observed that for those runs wherein the sum of carbon-forming potentials is 40F, longer operation was achieved than in those test runs where the sum of carbon-forming potentials was higher~
In a further series of test runs the following results Z- were obtained.
' ~
~:
, - .
. .
Case: ICR 2753 ~ 8971 TABLE I I
Sum of carbon Test forming potentials Length (F) (hrs.) Comments -20 382 No significant carbon accumulation 7 90 Very little, if any, carbon accumulation.
No carbon accumulation on catalyst A small, but significant amount of carbon accumulation on catalyst It will be observed that when the sum of carbon-forming potentials is lOF or less very minor amounts of carbon accumulation occur. At a value of 30F, small amounts of carbon had accumulated.
The test results above clearly show that when the sum of carbon-forming potentials is 40F~ or below, the carbon formation in the catalyst bed is minimized and it is further shown that when the sum of carbon-forming potentials is below about lOF, very desirable results are achieved.
~aving thus described the present invention, we claim:
: '
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for controlling carbon formation in a catalyst bed wherein carbon oxides are reacted with hydrogen to produce methane, the method consisting essentially of:
(a) determining the composition, temperature and pressure of the inlet reactant stream;
(b) determining the equilibrium reaction product stream composition, temperature and pressure based on the simultaneous equilibrium of the following reactions:
(1) CO + 3 H2 ? CH4 + H20 (2) CO + H20 ? CO2 + H2 (3) CO2 + 4 H2 ? CH4 + 2 H20;
(c) determining the reaction equilibrium constant for the reaction;
(4) 2 CO ? C + CO2 wherein W = equals the mol fraction CO2 in the equilibrium reaction product stream of (b), P1 = the pressure of the equilibrium product reaction stream of (b), and X = the mol fraction CO in the equilibrium reaction product stream of (b);
(d) determining the reaction equilibrium constant for the reaction (5) CH4 ? C + 2 H2 wherein Y = the mol fraction hydrogen in the equilibrium reaction product stream of (b), P1 = the pressure of the equilibrium reaction product stream of (b), and Z = the mol fraction methane in the equilibrium reaction product stream of (b);
(e) determining the equilibrium temperature (T1) in the reaction product stream;
(f) comparing the equilibrium temperature (Tl) in the reaction product stream to the equilibrium temperature (Tk1) corresponding to K1 of (c) and determining the carbon formation potential C1 which is defined as:
(6) Cl = Tkl - Tl;
g) comparing the equilibrium temperature in the reaction product stream to the equilibrium temperature (Tk2) corresponding to K2 of (d) and determining the carbon formation potential C2 which is defined as:
(7) C2 = Tl - Tk2;
(h) adding Cl and C2 to obtain a carbon deposition potential for the reaction; and (i) adjusting the composition, temperature and pressure of the inlet reactant stream so that the carbon deposition potential for the reaction is less than 40F°.
(a) determining the composition, temperature and pressure of the inlet reactant stream;
(b) determining the equilibrium reaction product stream composition, temperature and pressure based on the simultaneous equilibrium of the following reactions:
(1) CO + 3 H2 ? CH4 + H20 (2) CO + H20 ? CO2 + H2 (3) CO2 + 4 H2 ? CH4 + 2 H20;
(c) determining the reaction equilibrium constant for the reaction;
(4) 2 CO ? C + CO2 wherein W = equals the mol fraction CO2 in the equilibrium reaction product stream of (b), P1 = the pressure of the equilibrium product reaction stream of (b), and X = the mol fraction CO in the equilibrium reaction product stream of (b);
(d) determining the reaction equilibrium constant for the reaction (5) CH4 ? C + 2 H2 wherein Y = the mol fraction hydrogen in the equilibrium reaction product stream of (b), P1 = the pressure of the equilibrium reaction product stream of (b), and Z = the mol fraction methane in the equilibrium reaction product stream of (b);
(e) determining the equilibrium temperature (T1) in the reaction product stream;
(f) comparing the equilibrium temperature (Tl) in the reaction product stream to the equilibrium temperature (Tk1) corresponding to K1 of (c) and determining the carbon formation potential C1 which is defined as:
(6) Cl = Tkl - Tl;
g) comparing the equilibrium temperature in the reaction product stream to the equilibrium temperature (Tk2) corresponding to K2 of (d) and determining the carbon formation potential C2 which is defined as:
(7) C2 = Tl - Tk2;
(h) adding Cl and C2 to obtain a carbon deposition potential for the reaction; and (i) adjusting the composition, temperature and pressure of the inlet reactant stream so that the carbon deposition potential for the reaction is less than 40F°.
2. The method of Claim 1 wherein carbon deposition is minimized by adjusting said carbon deposition potential to a value less than l0F°.
3. The method of CLaim 2 wherein said carbon deposition potential is less than 0F°.
4. The method of Claim 2 wherein each of Cl and C2 is less than 10F°.
5. The method of Claim 4 wherein each of Cl and C2 is less than 0F°.
6. The method of Claim 1 wherein a differential pressure measuring means is used to determine the differential pressure across said catalyst bed.
7. The method of Claim 6 wherein said differential pressure is maintained substantially continuously.
8. The method of Claim 1 wherein carbon deposits are reduced by adjusting said carbon deposition potential to a value from 0 to -40F°.
9. The method of Claim 8 wherein said carbon deposition potential is from -10 to -40F°.
10. The method of Claim 9 wherein each of Cl and C2 is less than 0F°.
11. The method of Claim 10 wherein each of Cl and C2 is less than -10F°.
12. The method of Claim 1 wherein said carbon deposition potential is reduced by increasing the hydrogen/CO ratio in the inlet reactant stream.
13. The method of Claim 1 wherein said carbon deposition potential is reduced by decreasing the amount of carbon dioxide in the inlet reactant stream.
14. The method of Claim 1 wherein said carbon deposition potential is reduced by increasing the amount of water or steam in the inlet reactant stream.
15. The method of Claim 1 wherein said carbon deposition potential is reduced by increasing the hydrogen/CO ratio in the inlet reactant stream and by decreasing the amount of carbon dioxide in the inlet reactant stream.
16. The method of Claim 15 wherein said carbon deposition potential is reduced by increasing the amount of water or steam in the inlet reactant stream.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA306,146A CA1108971A (en) | 1978-06-23 | 1978-06-23 | Method for minimizing carbon formation on methanation catalysts |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA306,146A CA1108971A (en) | 1978-06-23 | 1978-06-23 | Method for minimizing carbon formation on methanation catalysts |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1108971A true CA1108971A (en) | 1981-09-15 |
Family
ID=4111758
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA306,146A Expired CA1108971A (en) | 1978-06-23 | 1978-06-23 | Method for minimizing carbon formation on methanation catalysts |
Country Status (1)
| Country | Link |
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| CA (1) | CA1108971A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015106824A1 (en) * | 2014-01-17 | 2015-07-23 | Haldor Topsøe A/S | Start-up procedure for a methanation process |
| CN110474073A (en) * | 2019-09-02 | 2019-11-19 | 潍柴动力股份有限公司 | Detect the method and device of carbon distribution inside solid oxide fuel cell system |
-
1978
- 1978-06-23 CA CA306,146A patent/CA1108971A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015106824A1 (en) * | 2014-01-17 | 2015-07-23 | Haldor Topsøe A/S | Start-up procedure for a methanation process |
| CN110474073A (en) * | 2019-09-02 | 2019-11-19 | 潍柴动力股份有限公司 | Detect the method and device of carbon distribution inside solid oxide fuel cell system |
| CN110474073B (en) * | 2019-09-02 | 2021-01-19 | 潍柴动力股份有限公司 | Method and device for detecting carbon deposition in solid oxide fuel cell system |
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